Synthesis, Antimicrobial Activity, DFT, Molecular Docking, and Dynamic Simulations of Trityl Mannopyranoside Derivatives for Potential Antibacterial Agents

Aim: There is an urgent need for new antimicrobial compounds with alternative modes of action for the treatment of drug-resistant bacterial and fungal pathogens.

Background: Carbohydrates and their derivatives are essential for biochemical and medicinal research because of their efficacy in the synthesis of biologically active drugs.

Objective: In the present study, a series of methyl α-D-mannopyranoside (MMP) derivatives (2-6) were prepared via direct acylation, and their biological properties were characterized.

Methods: The structures of synthesized compounds were established by analyzing their physicochemical, elemental, and spectroscopic data and evaluating their in vitro antimicrobial activities through in silico studies.

Results: In the antibacterial study, compound 3 was found to be mostly active toward most of the organisms, exhibiting maximum inhibition of S. abony and minimum inhibition of P. aeruginosa. However, the MIC and MBC values revealed that this compound is highly effective against Bacillus subtilis (MIC of 0.5 μg/L and MBC of 256 μg/L). In terms of antifungal activity, 3 and 6 showed the most promising activity toward Aspergillus flavus, with an inhibition of 95.90 ± 1.0% for compound 3 and 96.72 ± 1.1% for compound 6. Moreover, density functional theory (DFT) in conjunction with the BLYP/6-311G (d) basis sets was used to calculate the dipole moment and total energy for each compound, and the molecular electrostatic potential and Mulliken charge were considered to study the electrophilicity and nucleophilicity of the groups in each compound. For dipole moment calculations, the dipole moments are in the following order: 6 < 3 < 1 < 5 < 2 < 4, inferring that compounds 2 and 4 possess a high dipole moment in comparison with the other inhibitor systems. Furthermore, molecular docking was performed against threonine synthase from B. subtilis ATCC 6633 (PDB: 6CGQ) to identify the active site of the compounds, with compound 3 showing a maximum binding energy of -10.3 kcal/mol and compound 4 exhibiting a binding energy of -10.2 kcal/mol. In addition, a 100 ns MD simulation was performed, and the results revealed a stable conformation and binding pattern within the stimulating environment.

Conclusion: Our synthetic, antimicrobial, and in silico experiments revealed that MMP derivatives exhibit potential activity, providing a therapeutic target for bacteria and fungi.